X-ray crystal structure determination will be used to study the molecular conformations and modes of aggregation of lipids. The structures will include cholesteryl esters of fatty acids, cholesterol adducts with organic and inorganic compounds, phospholipids and their components. The aim will be to seek extrapolations at the molecular level concerning the lipid-lipid interactions which are important in the liquid crystalline state of lipids in biomembranes, serum lipoproteins and the fatty deposits in atherosclerotic lesions.